1. Field of the Invention
The present invention relates to a numerical controller of a laser beam machine having a function of controlling an operation of a nozzle of the laser beam machine to automatically retreat the nozzle from a workpiece surface during gap control of the nozzle or return the nozzle to the workpiece surface.
2. Description of the Related Art
It is necessary for a laser beam machine to hold the physical relationship between a nozzle and a workpiece within a predetermined range and thus, gap control to maintain the distance (gap amount) between the nozzle and the workpiece constant is carried out by controlling the distance between the nozzle and the workpiece.
In laser beam machining in which the gap control is carried out, the workpiece and the nozzle are positioned close to each other and thus, when the nozzle is moved at high speed for positioning with respect to the workpiece, interference with warping or deformation of a workpiece which is generated accompanying the machining or interference with obstacles on the workpiece surface generated accompanying the machining may occur. Thus, after stopping the gap control and issuing a command to cause a gap control axis to retreat in a direction away from the work, it is necessary to carry out positioning and also to activate the gap control when the machining is restarted.
Thus, as disclosed by Japanese Patent Application Laid-open No. 2004-001067 and the like, a method of starting a retreat operation of the gap control axis to a retreat position set simultaneously with the start of positioning, in the positioning during gap control, starting movement of a contouring control axis after the gap control axis retreats to a certain height, and causing the gap control axis to automatically return from the retreat position to the workpiece surface in time with the end of movement of the contouring control axis. With this method, commands to start and stop the gap control and to cause the gap control axis to retreat can be omitted, realizing efficient machining.
The movement of the nozzle according to a conventional technology will be described using FIG. 9.
When a nozzle 36 reaches a machining end point before movement and a positioning command is issued, a numerical controller (1) causes the nozzle 36 to retreat in a direction away from workpiece 39 and (2) starts movement to a contouring control axis when the nozzle 36 reaches a certain height. When the nozzle 36 reaches a retreat position, the numerical controller (3) stops the movement in the retreat direction and continues the movement in the direction toward the contouring control axis. Then, the numerical controller (4) causes the nozzle 36 to return to the surface of the workpiece 39 just when the contouring control axis reaches a positioning end point, and continues machining.
In the positioning operation control of the nozzle according to the conventional technology, obstacles near the nozzle position are avoided when the positioning operation is started by carrying out control such that, after starting the retreat operation of the nozzle, the contouring control axis waits to move for a certain time until the nozzle retreats to a certain height.
However, there are cases in which an obstacle that cannot be avoided even if the nozzle is retreated in a direction away from the workpiece surface between the machining end point and the next machining start point when the nozzle is positioned is present or the nozzle needs to be moved to the next machining start point via a particular position. In such cases, as shown in FIG. 10, the positioning operation needs to be specified in consecutive several blocks separately and if a plurality of consecutive positioning commands as described above is issued in the positioning operation control of the nozzle according to the conventional technology, the retreat/return of the nozzle is repeated for each positioning command block, posing a problem of a long machining time in proportion to the number of positioning commands caused by a waiting time until the movement start of the contouring control axis in a portion of (1) in FIG. 10.